It is known that rolls in a rolling mill flatten slightly due to rolling forces imposed on the working rolls and intermediate rolls as they are squeezed between the backing bearings and the material being rolled. Since the width of the strip material being rolled is always less than the length of the working rolls, the ends of the working rolls are not flattened by these forces and there is a transition area extending inward from the edge of the strip being rolled. This transition section causes the edges of the strip to be over-rolled at the edges. This is because the distance between the flattened work rolls in the central portion of the strip is greater than the distance between the partially flattened work rolls at the edge of the strip. A strip that is over-rolled at the edges will result in wavy or "pie crust" edges.
The prior art has sought to control the polarity of the rolled material in various ways, for instance by controlling the surface profile of the work rolls and intermediate rolls, by controlling the surface profile of the backup bearing rolls through hydraulic cylinders actuating eccentric shaft mounting, or by selective bending of rolls.
Currently, a popular method for adjusting the strip edge relief in a twenty-high cluster rolling mill is to employ a pair of intermediate rolls in contact with the upper work roll which are tapered on one end, and a pair of intermediate rolls in contact with the lower work roll, which are tapered on the other end. Then, by selectively shifting one or the other of the sets of tapered rolls in a lateral direction, using rotating couplings and linkage rods attached to hydraulic actuators, the degree of strip edge relief may be adjusted. The disadvantage of this system is that the rotating couplings must be small in diameter in order to function. Therefore lateral adjustments of the tapered rolls may only achieved under light rolling loads.
Although the prior art system utilizing lateral adjustments of the single-end-tapered intermediate rolls is effective for controlling over-rolling of strip edges, the lateral shifting mechanisms required are complicated and expensive. Also removal and replacement of the single-end-tapered intermediate rolls is cumbersome and time consuming.
Accordingly, one object of the present invention is to provide an improved method and apparatus for controlling strip edge relief in a cluster rolling mill.
Another object of the invention is to provide an improved method and apparatus for controlling polarity of strip material rolled in a twenty-high cluster rolling mill.
Still another object of the invention is to provide an improved method and apparatus for utilizing tapered intermediate rolls to adjust strip edge relief, without requiring lateral adjustment of the tapered rolls.